This application is based on Japanese Patent Application No. 2001-296056 filed on Sep. 27, 2001, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a flame-resistant and sound- and vibration-insulating member for vehicles, and a process of manufacturing the same, and more particularly, to a sound- and vibration-insulating member consisting of a soft polyurethane foam which has not only excellent heat resistance, but also high degrees of fire or flame resistance or retardancy and sound or noise absorbing property, and a process suitable for manufacturing such a sound- and vibration-insulating member.
2. Discussion of Related Art
Conventionally, vehicles such as automotive vehicles use various sound-insulating members for isolating or insulating noises to be transmitted to the outside of the vehicle body or to the inside of the vehicle compartments. In the engine room of the vehicle, for example, an engine cover, side covers, an oil-pan cover and an under cover are disposed around the vehicle engine, to reduce the amount of the noise to be transmitted from the engine, which is a source of the noise. Those covers are rigid members such as metallic sheets which are provided with foamed bodies such as foamed rubber or urethane fixed thereto, as disclosed in FIG. 1 of U.S. Pat. No. 6,237,717 B1. In the vicinity of the engine body of the vehicle, there are also disposed various devices and components, and gaps or spaces are inevitably left between the engine body and those devices and components. In operation of the engine, standing waves are generated in those gaps, and the noises generated by the engine are undesirably boosted. To attenuate or suppress the standing waves for thereby reducing the noises to be transmitted from the engine, JP-Y2-59-7545 proposes to fill the above-indicated gaps or spaces with noise insulators in the form of foamed bodies such as foamed rubber or urethane members, such that the noise insulators exist as spacers or fillers in the spaces between the engine body and the surrounding devices and components.
The foamed rubber or urethane material of such sound or noise insulators that are disposed in the vicinity of the engine body is required to exhibit high degrees of not only heat deterioration resistance but also flame or fire resistance. Although EPDM foamed bodies conventionally used as the foamed rubber members have a high resistance to heat deterioration, they suffer from a problem of insufficient flame resistance,or retardancy. On the other hand, foamed bodies of epichlorohydrin rubber also used as another type of foamed rubber members have a high degree of flame resistance, but suffer from insufficiency in the heat deterioration resistance.
Examples of the foamed urethane members used alternatively to the foamed rubber members are foamed polyurethane members foamed with asphalt such that the polyurethane foam is impregnated with the asphalt, as disclosed in JP-B2-57-22051 and JP-B2-61-50965. Described in detail, the asphalt-impregnated polyurethane foam is formed by filling a mold with a composition consisting of polyol, polyisocyanate, a foaming agent, an amine catalyst, a fire or flame retarder or retardant and asphalt, and foaming the composition into the asphalt-impregnated polyurethane foam. The thus formed asphalt-impregnated polyurethane foam is relatively economical to manufacture, and has a relatively high degree of heat resistance, but suffers from a potential problem of insufficiency of flame or fire resistance or retardancy. While the flame resistance of the asphalt-impregnated polyurethane foam can be improved by increasing the content of the flame retardant of the above-indicated composition, an increase in the content of the flame retardant inevitably results in an increase of cost of manufacture of the polyurethane foam, and the heat deterioration resistance and other properties of the foam are undesirably lowered. Accordingly, the asphalt-impregnated polyurethane foam having an increased content of the flame retardant is not acceptable.
JP-A-7-233236 discloses a noise insulating urethane foam which uses a styrene polymer as a polyol component and which includes a flame or fire retardant. The use of the styrene polymer together with the flame retardant material in an attempt to enable the polyurethane foam to exhibit high degrees of not only flame resistance but also heat deterioration resistance makes it difficult to manufacture the polyurethane foam at a low cost. Further, the heat deterioration resistance is satisfactory at 120xc2x0 C. or lower, namely, the flame retardant contained in the foam tends to scatter at a temperature exceeding 120xc2x0 C., undesirably resulting in a loss of flame resistance and/or reduction of the heat deterioration resistance of the polyurethane foam.
Further, JP-A-10-81142 discloses a vehicle vibration- and noise-insulating member which has excellent vibration and noise insulating properties and excellent waterproofing property. This vibration- and noise-insulating member is a foamed body (polyurethane foam) formed by a reaction between a polyolefin polyol having a skeleton of a saturated hydrocarbon resin as a polyol component, and an organic polyisocyanate component, in the presence of a surface active agent having a skeleton of fatty ester including a hydrophilic group. However, the above-indicated publication JP-A-10-81142 does not disclose any means for giving the polyurethane foam excellent flame resistance and heat deterioration resistance.
The present invention was made in view of the background art discussed above. It is therefore a first object of the present invention to provide a flame-resistant and sound- and vibration-insulating member for a vehicle, which exhibits high degrees of not only flame resistance but also heat deterioration resistance and which is improved in its sound absorbing property and economical to manufacture. A second object of this invention is to provide a process suitable for manufacturing such a flame-resistant and sound- and vibration-insulating member having excellent properties.
The first object indicated above may be achieved according to a first aspect of the present invention, which provides a flame-resistant and sound- and vibration-insulating member for a vehicle, comprising a soft polyurethane foam formed by a reaction between an organic polyisocyanate component and a polyol component, wherein the organic polyisocyanate component includes as a major component thereof a monomeric MDI which includes diphenylmethane diisocyanate and further includes a reaction product containing carbodiimide and/or uretone imine groups, said reaction product being obtained by carbodiimidizing isocyanate groups of diphenylmethane diisocyanate, said monomeric MDI containing 29-33% of NCO and including 1-45% by weight of 2, 4xe2x80x2-diphenylmethane diisocyanate in the form of a monomer and/or a carbodiimidization product, while the polyol component includes at least 50% by weight of polyol having 2-8 functional groups and a molecular weight of 1000-10000, and wherein the soft polyurethane foam has a density of 40-150kg/m3, a 50% compressive load of (5-60)xc3x9710xe2x88x922N/mm2, a tensile strength of at least 120 kPa and an elongation of at least 50%, and exhibits flame resistance under a flammability test according to FMVSS-302 (Federal Motor Vehicle Safety Standards, USA).
In the flame-resistant and sound- and vibration-insulating member of the present invention described above, the polyurethane foam which constitutes this material is characterized in that the polyurethane foam is formed by a reaction between the specific organic polyisocyanate component described above and the specific polyol component also described above. In this reaction, the activity and cross-linking property of the organic polyisocyanate component are effectively combined and balanced with those of the polyol component, making it possible to obtain a soft polyurethane foam which exhibits excellent physical properties before and after a heat deterioration test, and high degrees of fire or flame resistance or retardancy and formability.
In particular, the present invention uses as the organic polyisocyanate component a MDI-based polyisocyanate whose major component consists of diphenylmethane diisocyanate (MDI). The MDI-based polyisocyanate is a monomeric MDI including a reaction product containing at least one of carbodiimide group and uretone imine group. The reaction product is obtained by carbodiimidizing isocyanate groups of diphenylmethane diisocyanate, rather than a conventionally used polymeric MDI. The use of this monomeric MDI permits an effective improvement in the heat deterioration resistance of the obtained soft polyurethane foam, and effectively gives the foam a high degree of fire or flame resistance, without the addition of any conventionally used flame or fire retardant, so that the foam when exposed to a flame is melted down due to heat, and therefore prevents propagation of the flame.
Thus, the present invention has eliminated a need of including any flame retardant into the foam for the purpose of giving a flame resistance to the flame-resistant and sound- and vibration-insulating member for the vehicle. Accordingly, the present flame-resistant and sound- and vibration-insulating material is free of any of the various problems which would be caused by the use of a flame retardant in a large amount as experienced in the prior art, and which include a problem of an increase in the cost of manufacture of the foam.
According to one preferred form of the flame-resistant and sound- and vibration-insulating material of the present invention, a content of NCO in the monomeric MDI is held within a range of 30.5-32.5%, so that the present material exhibits the above-indicated advantages with increased stability.
According to another preferred form of the flame-resistant and sound- and vibration-insulating material of the invention, each of the tensile strength and the elongation of the soft polyurethane foam after a heat aging or deterioration test for 50 hours at 160xc2x0 C. is at least 50% of those before the heat deterioration test.
According to a further preferred form of the material of the present invention, the organic polyisocyanate component does not include a polymeric MDI consisting of a crude MDI having at least three benzene rings in a molecule, or includes the polymeric MDI such that a content of the polymeric MDI with respect to a sum of the monomeric MDI and the polymeric MDI is not larger than 5% by weight. According to this form of the invention, the object indicated above may be more advantageously achieved.
The second object indicated above may be achieved according to a second aspect of this invention, which provides a process of manufacturing a flame-resistant and sound- and vibration-insulating member for a vehicle, comprising a soft polyurethane foam formed by a reaction between an organic polyisocyanate component and a polyol component, the process comprising the steps of preparing the organic polyisocyanate component such that the organic polyisocyanate component includes as a major component thereof a monomeric MDI which includes diphenylmethane diisocyanate and further includes a reaction product containing carbodiimide and/or uretone imine groups, the reaction product being obtained by carbodiimidizing isocyanate groups of diphenylmethane diisocyanate, the monomeric MDI containing 29-33% of NCO and including 1-45% by weight of 2,4xe2x80x2-diphenylmethane diisocyanate in the form of a monomer and/or a carbodiimidization product thereof, preparing the polyol component such that the polyol component includes at least 50% by weight of polyol having 2-8 functional groups and a molecular weight of 1000-10000; and causing a reaction between the organic polyisocyanate component and the polyol component, to form the soft polyurethane foam, such that a NCO/OH index is held within a range of 0.6-1.2.
The method according to the second aspect of this invention described above permits easy and economical manufacture of the flame-resistant and sound- and vibration-insulating member for the vehicle, with a high degree of formability and so as to give the material excellent properties as described above with respect to the first aspect of the invention.
According to one preferred form of the second aspect of the present invention, the reaction between the polyisocyanate component and the polyol component takes place in the presence of a foaming agent, so that the reaction to form polyurethane and foaming of the polyurethane take place concurrently, permitting efficient manufacture of the desired flame-resistant and sound- and vibration-insulating material with excellent properties.